Abstract

Through a series of simulations and experiments, we demonstrate that the frequently cited criterion of matching speckle size to detector element (pixel) size in laser speckle contrast imaging (LSCI) has the detrimental effect of reducing the contrast and thereby decreasing the variation in the laser speckle contrast image. Unlike quasi-elastic light scattering, where this matching condition has been shown to maximize the signal-to-noise ratio, in LSCI, the minimum speckle size must exceed the Nyquist criterion in order to maximize the contrast of the speckle patterns.

Results of the simulations (stars), imaged speckle experiments (circles), and objective speckle experiments (diamonds). In all cases, the effect of sampling the speckle pattern so that the speckle-to-pixel matching condition was met resulted in an approximately 20%–30% decrease in the calculated global contrast from the theoretical maximum of 1.0.

Intensity PDFs of the speckle pattern at different values of N. The dashed–dotted line is the theoretical PDF for a fully developed speckle pattern exhibiting negative exponential intensity statistics. When the speckle pattern was sampled at or above the Nyquist rate (N=2, 4, and 8), the PDF closely resembled the theoretical distribution. When the speckle pattern was undersampled (N=1.0, 0.5, and 0.25) the PDFs departed substantially from exponential statistics.